1. Field of the Invention
This invention relates to a film thickness detector for determining thickness variations in motion picture film corresponding to splices, torn edges, burned spots or torn sprocket holes in the film.
2. Description of the Prior Art
It is desirable to detect variations in thickness of film strips due to splices, burned spots or foreign material on the film. It is also desirable to detect cut edges or torn sprocket holes. It has been proposed to use light detector systems for determining the thickness of a film strip by use of a light beam which is tangent to a portion of the film surface and parallel with the longitudinal axis of the film strip. With such a system, however, the thickness of only a narrow central portion of the film strip is measured. Furthermore, it is difficult to provide an apparatus which can clean the light detector transmission and reception elements with such a longitudinal arrangement.
It has also been proposed to provide a light source directed toward a surface of a film strip such that a light beam will be reflected off the surface and received by a light detector. Such a system will not measure the thickness of film, but only discontinuities in the film which disperse the light beam.